Node Cloning / Duplication
At first I thought "well, one way would be to use something like a "texture.jpg" name for that texture, and simply change the file that is named like that... that would do the trick, somehow. Other than that, you could probably need to script the change, for all the nodes to load the same texture. I can't think of other ways, atm"... 

but then it came to my mind another trick, that could work better for you... here it is: use node groups!

you can set up a simple "image texture node" as a group, by itself. 



It sounds absurd, to make a group of just one node, but it isn't: because you can reuse groups on every material you choose, and link it differently to other nodes. 

Just select it as Add => Group => "yourGroupName" in the node composition area, and by default it has the same inputs/outputs as the base Texture Image node...

And, when you edit the group (on any node where it's used) you can change the texture, in a single node that's reused:



and, thus, reach your goal: